Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
8 results
Search Results
Item Influence of feed form and age of broilers on energy utilisation of feed ingredients : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science (Poultry Nutrition) at Massey University, Palmerston North, Manawatu, New Zealand(Massey University, 2022) Khalil, Mahmoud MohamedThe accurate determination of the available energy of feed ingredients is crucial to optimise their inclusion in feed formulations and to improve the profitability and sustainability of poultry production. The metabolisable energy (ME) is commonly used for energy evaluation and formulating the diets for poultry. However, there are some limitations and several factors that influence the precision of the evaluation of the ME content of feed ingredients and diets. The current thesis investigated some of the unexplored research gaps on the ME of the commonly used feed ingredients in broiler diets. The first study presented in Chapter 3 was conducted to investigate the influence of feed form (FF; mash vs. pellet) on the apparent metabolisable energy (AME) and nitrogen-corrected AME (AMEn) of 7 single feed ingredients, four cereal grains (wheat, sorghum, barley, and maize) and three protein sources (soybean meal; SBM, canola meal; CM, and meat and bone meal; MBM). The influence of broiler age AMEn of cereal grains was investigated in Chapter 4 (direct method) and Chapter 5 (substitution method). The fourth experiment reported in Chapter 6 examined the effect of broiler age on the AMEn of protein sources. The experiments discussed in Chapter 7 were unique in that a novel methodology was developed for the quantification of the ileal endogenous energy losses (IEEL) in broiler chickens and for the correction of apparent ileal digestible energy (AIDE) to true (TIDE) ileal digestible energy of cereal grains (wheat, sorghum, barley and maize). The last trial of the thesis reported in Chapter 8 was conducted to refine-tune the IEEL methodology developed in Chapter 7 and to determine the influence of age and dietary cellulose contents on the IEEL estimates in broiler chickens. Data reported in Chapter 3 demonstrated that FF influenced the AMEn of feed ingredients. Pelleting increased the AMEn of all cereal grains by an average of 0.22 MJ/kg. However, for protein source ingredients, FF influence was ingredient-dependent. Pelleting increased the AMEn of CM by 0.57 MJ/kg, had no effect on that of SBM and decreased the AMEn of MBM by 0.56 MJ/kg. The experiment reported in Chapter 4 investigated the influence of broiler age on the AMEn of cereal grains using the direct method. The assay diets were formulated with an inclusion of 962 g/kg of each grain in the diet and pelleted. The data revealed that the age of broiler chickens has a significant impact on the AMEn of cereal grains. The first week of age recorded the highest AMEn for all cereal grains. Thereafter, the AMEn decreased either linearly (sorghum) or quadratically (wheat, barley and maize) with the advancing age of broilers. In the study reported in Chapter 5, the effect of broiler age on the AMEn of cereal grains, from the same batches used in Chapter 4, was examined using the substitution method. A maize-SBM basal diet was formulated and test diets were developed by replacing (w/w) 300 g/kg of the basal diet with each cereal grain. The results showed that the effect of broiler age on the AMEn varied depending on the grain type. Whilst the AMEn of barley and maize were unaffected by age, the AMEn of wheat and sorghum increased with the advancing age of broiler chickens. The determined AMEn values differed between direct and substitution methods, with the substitution method generating lower AMEn values. Data reported in Chapter 6 demonstrated that the AMEn content of SBM and CM was influenced by age of broilers. The first week showed the highest AMEn value for both SBM and CM, followed by reductions for both ingredients up to week 3 and increases thereafter. The studies reported in Chapter 7 present a novel approach to quantify the IEEL in broilers and correct the AIDE of cereal grains (wheat, sorghum, barley and maize) to TIDE enabling comparisons with AMEn. The IEEL was estimated to be 1.45 MJ/kg dry matter intake (DMI) in 21-d old broilers, following the feeding of a glucose-based purified diet and used to calculate the TIDE. The apparent ileal digestibility of dry matter, nitrogen and starch were positively and highly correlated with the TIDE than the AIDE or AMEn. The studies reported in Chapter 8 were conducted to refine the proposed methodology for the estimation of IEEL proposed in Chapter 7 and to investigate the influence of age of broilers and the dietary cellulose contents on IEEL estimates. It was found that the age of broilers had no impact on the IEEL estimates. The IEEL was affected by the cellulose content and the IEEL increased from 0.37 MJ/kg DMI for the diet without cellulose to 1.80 MJ/kg DMI for the diet with 75 g/kg inclusion of cellulose. The findings reported in the current thesis demonstrate that the application of AMEn values determined based on assays using mash diets might result in over- or under-estimation of the available energy content of ingredients in commercial pelleted broiler diets and highlights the need for the use of pelleted diets in energy evaluation assays. The findings also revealed that the effects of age and methodology are relevant in the determination of AMEn of feed ingredients and question the validity of using single AME or AMEn values for feed ingredients in broiler diet formulations across different ages. Another notable contribution was to develop a novel approach to quantify the IEEL in broiler chickens for the first time. The thesis research also provides preliminary data on the TIDE of common cereal grains and highlights the possibility of applying the TIDE as an alternative to the ME system in poultry feed formulation.Item Studies on the measurement of calcium digestibility in raw materials for poultry and of digestible calcium requirement of broiler starters : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science (Poultry Nutrition) at Massey University, Palmerston North, Manawatu, New Zealand(Massey University, 2021) David, Laura ShiromiThe measurement of calcium (Ca) digestibility in feed ingredients for poultry is receiving increasing attention because of recent interest in formulating diets based on digestible phosphorous (P) and the close relationship between these two minerals in their absorption and post absorptive utilisation. Data on the ileal Ca digestibility of Ca sources and factors influencing Ca digestibility in poultry are scant. The current thesis presents follow-up studies of the previous work conducted at Massey University. The Ca digestibility values of Ca sources determined in the thesis, along with previous published data, were then used to develop dietary treatments to assess the digestible Ca requirement of broiler starters. The first study reported in Chapter 3 was conducted to examine the effect of basal diet composition on true ileal Ca digestibility of four Ca sources namely, limestone, meat and bone meal (MBM), monocalcium phosphate (MCP) and dicalcium phosphate (DCP) in broiler chickens. Two basal diets, namely a maize-based diet and a maize-starch-based purified diet, with each Ca source were tested. The results showed that the average true ileal Ca digestibility was higher in the maize-based diet (0.46) than that in the purified diet (0.37). True ileal Ca digestibility of limestone, MBM, MCP and DCP were determined to be 0.51, 0.41, 0.43 and 0.32, respectively. In the study reported in Chapter 4, the effect of dietary indicator-type and dietary adaptation length on the apparent ileal Ca digestibility of limestone were evaluated. In Experiment 1, the use of two indicators namely, titanium dioxide and acid insoluble ash (Celite) were compared and the findings showed that the ileal Ca digestibility was unaffected by dietary indicator. In Experiment 2, four dietary adaptation lengths namely, 24, 72, 120 and 168 hours were examined and it was found that the Ca digestibility was unchanged between 72 and 120 hours but decreased at 168 hours of adaptation length. The third study, presented in Chapter 5, was conducted to measure the influence of age (7, 14, 21, 28, 35 and 42 days post-hatch) on the Ca digestibility of limestone for broiler chickens. The findings revealed that the apparent ileal Ca digestibility coefficients were linearly decreased from day 7 to day 42. The ileal Ca digestibility coefficients were determined to be 0.51, 0.53, 0.36, 0.34, 0.41 and 0.27 at days 7, 14, 21, 28, 35 and 42, respectively. A secondary objective of this study was to examine the influence of dietary crude protein concentration (79 and 153 g/kg) on the apparent ileal Ca digestibility at 21 days of age. It was found the apparent ileal Ca digestibility was not influenced by dietary protein concentrations. The studies reported in Chapter 6 were conducted to measure the influence of phytase doses (0, 500 and 2000 FTU/kg) on the Ca and P digestibility of soybean meal (SBM) and canola meal (CM) in broiler starters (Experiment 1) and finishers (Experiment 2). True ileal Ca digestibility coefficients of SBM and CM, with no supplemental phytase, were determined to be 0.51 and 0.53, respectively, for broiler starters and 0.33 and 0.22, respectively, for broiler finishers. True ileal P digestibility coefficients of maize-SBM diet and maize-CM diet, with no phytase were determined to be 0.89 and 0.66, respectively, for broiler starters and 0.82 and 0.57, respectively, for broiler finishers. Microbial phytase increased the true ileal digestibility of Ca and P in maize-SBM diet and maize-CM diet, but the effect was more pronounced for the maize-CM diet. Superdosing of phytase (2000 FTU/kg) increased the Ca digestibility in CM and SBM by two-fold compared to the normal phytase dose (500 FTU/kg). The studies reported in Chapter 7 were conducted to determine the ileal Ca digestibility coefficients of two limestone sources in broilers and layers. The results showed that, in both sources, the apparent ileal Ca digestibility of limestone was found to be higher in laying hens (0.62 and 0.70) compared to broilers (0.50 and 0.43). The findings indicated that laying hens absorb Ca more efficiently than broilers which may be attributed to their high demand of Ca for eggshell formation. Using Ca digestibility values of Ca sources measured in this thesis work and previous published data, a growth study (Chapter 8) was conducted to estimate the standardised ileal digestible (SID) Ca requirement for 1 to 10 day-old broilers fed different dietary concentrations of both SID Ca (3.3, 3.9, 4.4, 5.0 and 5.5 g/kg) and SID P (4, 5 and 6 g/kg). Based on response surface models, the growth performance, bone mineralisation and mineral utilisation of broiler starters were found to be optimised at 5 g/kg SID P concentration. The concentrations of SID Ca that maximised body weight gain, tibia ash, tibia Ca, tibia P and toe ash were estimated to be 3.32, 4.51, 4.72, 4.36 and 4.78 g/kg, respectively, which corresponds to SID Ca to SID P ratios of 0.66, 0.90, 0.94, 0.87 and 0.96, respectively. Bone mineralisation required more SID Ca than for growth. Most of the findings reported in this thesis are novel and contribute to the advancement of current knowledge on the measurement of ileal Ca digestibility in poultry and the factors influencing Ca digestibility. The array of factors examined were hitherto unexplored and included the effects of basal diet type, dietary adaptation length, broiler age, phytase dose, Ca source and bird type (broilers vs. layers). Another notable contribution was to establish the requirements of digestible Ca, digestible P and the ratio of digestible Ca to digestible P for broiler starters (1-10-day old).Item Genetic and genomic studies of animal welfare and environmental traits in dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand(Massey University, 2020) Ariyarathne, Hewa Bahithige Pavithra ChathurangiNew Zealand dairy cows graze outdoors throughout the year and are exposed to a wide range of weather conditions also their excreta are dispersed in the paddock. There is an emerging interest in whether between-cow genetic variation could contribute to environmental sustainability and improved animal welfare. The initial objectives of the study were 1) to estimate genetic parameters of rectal temperature (RT) as an indicator of heat stress (HS), 2) to identify gene regions associated with HS through genome-wide association studies (GWAS), and 3) to estimate response of genetic selection for low HS on milk production using conventional selection in grazing dairy cows of New Zealand. The genetic variance of RT estimated in 776 mixed-breed cows at two Massey University experimental dairy farms was very low due to insufficient environmental stress on sampling days. This outcome diverted the topic of study to the genetic basis of milk urea concentration (MU) and efficiency crude protein utilisation (ECPU) and their potential role in improved environmental sustainability. The new study was conducted considering MU as the trait of interest. Additionally, the possible reduction of urinary nitrogen (N) excretion by genetic selection for low milk urea N concentration (MUN) was determined. The heritability estimated for MU (from 0.27 to 0.49) and ECPU (from 0.02 to 0.41) using a random regression model in 634 mixed-breed cows indicated that these traits can be genetically manipulated by direct selection. Estimates of genetic correlations between MU and yield of milk, fat, crude protein, lactose, and liveweight (LWT) in each day of ii lactation were mostly positive and imply that selection for reduced MU would result in reduced production and LWT of cows. The GWAS identified six novel genes (GMDS, E2F7, SIAH1, SLC24A4, LGMN, ASS1) associated with MU that function in protein catabolism, urea cycle, ion transportation and N excretion. This suggests that genomic selection for MU is possible, however, the results should be validated with a larger sample size. Selection index theory was used to estimate correlated responses for different selection indices including MUN with different relative emphasis (RE). The predicted genetic responses per cow per year of the current index were 16.4 kg milk yield (MY), 2.0 kg fat yield (FY), 1.4 kg crude protein yield (CPY), -0.4 kg LWT and -0.05 mg/dl MUN. Including MUN in the selection index with 20% negative RE resulted in annual responses of 5.4 kg MY, 1.6 kg FY, 1.0 kg CPY, -1.1 kg LWT and -0.17 mg/dl MUN. The total N predicted to be excreted in the base year was 336.5 kg/ha. When stocking rate was adjusted by changes in milk production and cow feed requirements, 10 years of selection with a selection index not including MUN increased total N excretion to 338.9 kg/ha. A selection index with 20% negative RE for MUN increased total N excretion to 341.6 kg/ha, and genetic gain in production of milk protein per hectare was reduced, thereby reducing farm profits. The results of this thesis indicate that inclusion of MUN in a selection index with negative RE is not an effective pathway to reduce farm-level N leaching and carbon footprint.Item Genetics of feed intake and efficiency in grazing dairy cows : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science(Massey University, 2017) Hurley, Alan MichaelFeed efficiency in dairy cows is widely acknowledged as a highly desirable characteristic to improve because of its well-documented impact on production costs. Traditional measures of feed efficiency have used ratio traits, specifically energy conversion efficiency, but these have undesirable statistical properties. Alternative measures of feed efficiency are those based on the residuals from regression-type statistical models, the most common of which is residual energy intake (REI). Residual energy intake is defined as the difference between actual and predicted intake and is usually derived from least squares regression models. The general objective of this thesis was to quantify phenotypic and genetic (co)variances between the feed intake complex, performance, and fertility traits in lactating Holstein-Friesian dairy cows. A total of 8,199 feed intake records from 2,693 lactations on 1,412 grazing lactating Holstein-Friesian dairy cows from experimental farms were used. Several alternative efficiency definitions were developed, each with their own respective strengths and weaknesses. Exploitable genetic variation was demonstrated to exist for the range of alternative efficiency traits, and the magnitude of this variation was sufficiently large to justify consideration of the feed efficiency complex in future dairy breeding goals. The heritability estimates for the different efficiency traits estimated using repeatability models varied from 0.06 to 0.21. Variance components, however, differed across lactation when estimated using random regression models; for example, the heritability of REI varied from 0.04 (34 DIM) to 0.11 (280 DIM) across lactation. Phenotypic correlations among many traits including REI and energy balance (EB) differed not only by stage of lactation but also by cow parity. Moderate to strong genetic correlations existed between REI and EB across lactation (ranging from 0.45 to 0.90). Albeit associated with large standard errors, estimated genetic correlations between feed efficiency and reproductive performance were either neutral or favourable suggesting greater genetic merit for feed efficiency does not appear to be antagonistically genetically correlated with reproductive performance. Selection index calculations using the current economic weights in the Irish Economic Breeding Index, and genetic (co)variances estimated in this thesis, indicate that the inclusion of REI in the index with an economic weight of €0.078/UFL will generate animals with improved REI.Item The comparison of supplements for young calves grazing autumn pasture: a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University(Massey University, 1987) Wittayanuparpyuenyong, KasetThirty two autumn-born calves (sixteen bull and sixteen heifer calves) were used to compared the effects of alternative supplements on performance, health, herbage intake and feed efficiency of young calves. 1. Four bull and four heifer calves in each of four blocks,which had previously received milk ad libitum,were randomly allocated to each of the four treatments at 5-6 weeks of age. The supplements of liquid milk, dry milk and concentrates were calculated to provide 11.28 MJME metabolisable energy (ME) (for ruminants) and 175 g crude protein (CP) daily and were fed for 5 weeks. Supplements were offered once a day and amounts eaten were measured. The control group was weaned directly onto autumn pasture. 2. Calves were grazed in the same paddocks,predominantly ryegrass and white clover,divided into four equal areas by two electric wires. Individual paddocks were used in rotation for 4-5 days and calves offered a daily herbage allowance of approximately 60 g DM per kg liveweight. After the experimental period the calves were grazed on pasture together in two mobs, bulls in one and heifer calves in the other, and liveweights measured until about 33 weeks of age. 3. The DM intake of supplement and herbage by individual calves were estimated indirectly using faecal markers (Chromic oxide and Polyethylene glycol). 4. Calf growth rates at various stages were measured. Feeding of supplements significantly (P<0.001) increased the liveweight gains of young calves grazing autumn pasture (control 257.1 g/d). Among the supplemented calves, calves receiving liquid milk had a significantly (PItem Effect of differences in live weight on feed requirements of pregnant non-lactating grazing dairy cows : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University, Palmerston North, New Zealand(Massey University, 1994) Garćia-Muñiz, J GThe effect of differences in live weight (LW) on feed requirements of pregnant non-lactating cows was assessed during a 41-day grazing experiment. Thirty eight dry pregnant Friesian and Jersey cows (28 Friesian cows differing in live weight and 10 Jerseys) at similar stages of pregnancy (range 190 to 230 days pregnant) and averaging 5.8 years of age were used. The cows were grouped according to their initial LW in three size-groups, i.e. Big Friesians (BF; n=14, LW = 526 kg), Small Friesians (SF; n=14, LW = 415 kg) and Jerseys (J; n=10, LW = 362 kg). Within each size-group the cows were randomly allocated to one of two levels of daily herbage dry matter (DM) allowance (HA), calculated to meet either maintenance and pregnancy (i.e. HA of 7.7 to 11.0 kg DM/cow/day), or the gain of 1 kg of maternal live weight above maintenance and pregnancy (i.e. HA of 17.1 to 22.5 kg DM/cow/day). The cows provided individual records of their daily liveweight gain (LWG, kg/cow), total liveweight gain (ΔLW) and total condition score change (ΔCS) achieved during the 41-day experimental period. Group average herbage dry matter intake (DMI) and herbage DM allowance were calculated for each treatment group from herbage mass (HM) assessed by cutting-washing-drying and weighing, and by means of two calibration equations, one for each level of feeding, relating HM to the average of 30 plate meter readings (PMR) taken every day before and after grazing. These two calibration equations were: (1) for the ad libitum level of feeding: HM (kg DM/ha) = 764.0 (s.e. 212.0) + 158.0 (s.e. 12.7) * PMR (r = 0.98; CV = 24%; r.s.d. = 548 kg DM), and (2) for the maintenance fed cows: HM (kg DM/ha) = 171.0 (s.e, 3.5) * PMR (r = 0.98; CV = 21.6%; r.s.d. = 442 kg DM). The energy content of the herbage (MJ ME/kg DM) apparently grazed by the cows and their metabolizable energy intake (MEI) were calculated from the in vitro digestibility analyses of pasture samples plucked randomly from each of the grazing areas. Least squares means were calculated for group average herbage dry matter intake (DMI), herbage DM allowance (HA), metabolizable energy intake (MEI), and for the variables derived from the animals' performance (ΔLW, LWG, ΔCS) and differences between levels of feeding and size-groups were tested for significance using analysis of variance. Differences in average live weight between the three size-groups were highly significant (P<0.001) throughout the experimental period (i.e. BF = 552 kg; SF = 442 kg; J = 377 kg). Heavier cows had: (1) significantly higher daily herbage DM allowances (BF, 16.7; SF, 14.4; J, 12.4 kg/cow/day); (2) higher daily DMI (BF, 10.2; SF, 8.6; J, 7.5 kg/cow/day); (3) higher MEI (BF, 117; SF, 100; J, 87 MJ/cow/day), and (4) lower stocking densities (BF, 240; SF, 262; J, 305 cows/ha/24 hours). However, when HA, DMI and MEI where expressed on a metabolic weight basis, none of these variables were significantly different between the three size-groups. From the least squares means of LWG, ΔCS, DMI and MEI calculated for each treatment group, feed requirements for zero ΔCS or maintenance (i.e. MEm) and feed requirements for ΔCS were calculated by means of linear regression analyses. The MEm calculated pooling the three size-groups was 0.648 MJ ME/LW0.75/day for zero ΔCS; and an average intake of 167 kg DM or 1986 MJ ME/cow above maintenance was required for the gain of one condition score unit/cow during the 41 days of experimental period, which was equivalent to a total liveweight change of 52.7 kg/cow. From these estimates it was calculated that cows heavier by 100 kg required an extra intake for maintenance of 10.5 MJ ME/cow/day or about 0.95 kg herbage dry matter intake/cow/day. The results of the present experiment were used to assess the effect of farming large-size cattle on the productive efficiency of pasture-based dairy systems.Item How seasonal dairy farmers in the Lower North Island of New Zealand achieve high per cow production : a participatory case-study : a thesis presented in partial fulfilment of the requirements of the degree of Master of Agricultural Science in Farm Management, at Massey University, Palmerston North(Massey University, 1996) Crawford, H KNew Zealand's 14,000 seasonal dairy farmers supply 16 co-operative companies that operate 40 milk processing factories. While the industry produces only 1.5% of the world's milk, it supplies 25% of the world trade in dairy products, which was worth $5 billion to the New Zealand economy in 1994/95. In order to remain internationally competitive, dairy production research in New Zealand has focused on achieving 'low cost' milk production from pasture. Recent high prices for dairy land and the need to reduce the seasonality of milk supply have promoted greater interest in increasing per cow production. Greater milk yields per cow would allow greater utilisation of the genetic potential of the New Zealand dairy cow for milk production and reduce per cow costs for non-feed items. At present only 1% of seasonal supply dairy farmers consistently achieve in excess of 350 kg milksolids (MS) per cow per year. These farmers achieve this level of production with resources that appear to be similar to those of other dairy farmers, but little is known about how these resources are managed to consistently achieve high per cow production. The objective of this research was to describe the management processes used by farmers who achieve high per cow production. Milk supply records from Tui Milk Products Limited were used to identify seasonal dairy farmers who had averaged 350 kg MS/cow/year for at least three seasons (n=31). All of these farmers were surveyed by telephone to obtain information about themselves and their farms. A sub-sample of ten farmers was then chosen from this group for in-depth study and of these 8 farmers agreed to participate. Through three semi-structured interviews, each farmer was asked to describe their management processes. The interviews were recorded, transcribed verbatim and analysed using the NUD.IST computer program to identify concepts associated with high per cow production. A 'model' of a high per cow production system was developed from these concepts and this was compared with the recommendations in the literature. The results suggest that while the resources available to the farmers influenced per cow production, they did not constrain the achievement of high per cow production. Farmers strategically managed the resources available to enable them to achieve high production levels and used tactical adjustments to account for seasonal variation in pasture production and feed demand. All of the case-farmers reared their herd replacements 'well', concentrated on fully feeding the herd throughout lactation, and had superior pasture management systems in place. In addition, these farmers were genuinely interested in the state of their farms, particularly their livestock, and closely observed livestock behaviour as part of their management system.Item Relationships between behavioural traits, residual feed intake, and average daily gain in growing dairy heifers fed lucerne cubes : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Palmerston North, New Zealand(Massey University, 2012) Green, Talia CorinaResidual feed intake (RFI) is a measure of an individual’s efficiency in utilising feed for maintenance and production during growth or lactation. It can be defined as the difference between the actual and predicted feed intake of that individual. Efficient animals eat less than predicted for their body weight and level of performance, and inefficient animals eat more. The objective of this study was to investigate possible relationships between RFI and behavioural traits, such as feeding behaviour, social dominance, and activity in young dairy heifers. The intakes and liveweights of 1049 growing dairy heifers (6-8 months of age, 195 ± 25.8 kg liveweight) in five cohorts were measured for 42-49 days to ascertain individual RFI. Animals were housed in an outdoor feeding facility comprising 28 pens, each with eight animals and one feeder per pen, and were fed a dried, cubed lucerne diet. An electronic feed monitoring system measured the intake and feeding behaviour of individuals. Intake was moderately to strongly correlated with RFI for individual cohorts (r = 0.54-0.74; p < 0.001), indicating that efficient animals ate less than inefficient animals. Several other feeding behaviour traits were related to RFI, but the relationships were weak (r = 0.14-0.26; p < 0.05) suggesting that feeding behaviour is not a reliable predictor of RFI in growing dairy heifers. Statistical comparison of the extremes of RFI (104 most and 104 least efficient) showed that the most efficient animals (low-RFI) had similar liveweight and average daily gain to the least efficient (high-RFI) (p > 0.05) but ate less (mean ± SED; 6.97 v 8.75 ± 0.10 kg cubes), had fewer meals (6.3 v 8.2 ± 0.61/d), shorter daily feeding duration (2.71 v 2.85 ± 0.07 h), ate longer meals (35.6 v 30.6 ± 1.54 min/meal), and ate more slowly (45.4 v 53.0 ± 1.36 g cubes/min) than the least efficient animals (all p < 0.05). These groups also differed in their feeding patterns over 24 h. Video recordings of 32 animals showed that daily activity included (mean ± SEM) 15.4 ± 0.5 h lying, 4.8 ± 0.5 h standing, and 2.9 ± 0.1 h feeding. However, neither social status nor activity were related to RFI in this study (p > 0.05). Feeding behaviour explained only a small proportion of the variation in RFI in dairy heifers. Selecting animals for low RFI (efficient) is unlikely to affect social dominance and activity, although these results should be confirmed in a grazing environment representative of most New Zealand dairy farms.